1. Field of the Invention
The present invention relates to a vaporized fuel processing device for an internal combustion engine, and more particular to a vaporized fuel processing device capable of separating vaporized fuel in accordance with load conditions of the engine to thereby suppress fluctuations in the fuel-air ratio and prevent a deterioration of an adsorbent in a canister.
2. Description of Related Art
There has been known a vaporized fuel processing device in which fuel vapor generated in a fuel tank of automobiles is provisionally adsorbed in a canister and then the adsorbed fuel vapor is subjected to a separation (which will be hereinafter as to xe2x80x9cpurgexe2x80x9d) process to be sucked in an engine when operated, and the fuel vapor burns in the engine. Such the device is disclosed in for example Japanese patent unexamined publication No. 8-284765. The device of this Japanese publication is constructed so that a purge passage for delivering the fuel vapor desorbed from an adsorbent provided in the canister to an air intake pipe of the engine can be changed over from one passage having a small opening area to the other having a large opening area, and vice versa. An appropriate purge passage is selected between the two passages based on an operating state of the engine and a concentration of the fuel vapor. A purged amount of the fuel vapor is controlled to a desired value by a flow rate control valve interposed in the downstream of the purge passages.
In the canister of the above device, however, the purge passages are arranged contiguously to a tank port through which vaporized fuel flows into the canister from a fuel tank. In the case where a large amount of vaporized fuel is generated in the fuel tank under high temperature conditions and the like, therefore, the concentration of the vaporized fuel to be sucked in the engine suddenly changes, resulting in excessive concentrations and fluctuations in the fuel-air ratio. This possibly may cause deterioration in a constituent of exhaust gas and reduction in operability of the engine. Since only a single passage is provided for supplying fuel vapor from the fuel tank to the canister, all the fuel vapor, in a small or large amount, is surely adsorbed in the adsorbent. As the number of repetitions of adsorption and purge increases, the degradation of the adsorbent is accelerated, thereby causing deterioration in the treatment or process capability of the canister.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a vaporized fuel processing device capable of controlling the concentration of fuel vapor to be sucked in an engine from a canister which adsorbs the fuel vapor, thereby preventing fluctuations in a fuel-air ratio at burning of the fuel vapor in the engine, and also capable of preventing degradation of an adsorbent in the canister.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a vaporized fuel processing device for processing to supply vaporized fuel generated in a fuel tank to an engine, the device including: a canister connected to the fuel tank and accommodating an adsorbent for adsorbing the vaporized fuel delivered from the fuel tank; first control means disposed between the fuel tank and the canister, the first control means being operated to supply the vaporized fuel to the canister when a pressure of the vaporized fuel in the fuel tank is a first predetermined pressure or below; second control means disposed between the fuel tank and canister, the second control means being operated to supply the vaporized fuel to the canister when the pressure of the vaporized fuel in the fuel tank exceeds a second predetermined pressure that is larger than the first predetermined pressure; and a control valve disposed in a passage through which the vaporized fuel is supplied from the canister to a throttle body.
According to another aspect of the present invention, there is provided a canister including: an adsorbent chamber which accommodates an adsorbent; a partition wall for dividing the adsorbent chamber into a first and second chambers; a purge port section and a first tank port section, each having an end opened to the first chamber; an atmosphere port section having an end opened to the second chamber; and a second tank port section having an end opened to any one of the first and second chambers.